1. Field of the Invention
The present invention relates to an air-conditioning apparatus employing a coolant or refrigerant heater (hereinafter referred to as refrigerant heater) in achieving a refrigerating cycle, and particularly to a refrigerant heating air-conditioning apparatus employing a two-cylinder compressor.
2. Description of the Prior Art
A heat pump air-conditioning apparatus usually forms a refrigerating cycle with a compressor, an indoor heat exchanger, an outdoor heat exchanger, and an expansion valve. During a heating operation, the indoor heat exchanger discharges heat out of coolant or refrigerant (hereinafter referred to as refrigerant), the expansion valve reduces the pressure of the refrigerant, and the outdoor heat exchanger lets the refrigerant absorb atmospheric heat and evaporate. The evaporated refrigerant is sent to the compressor.
In this way, the heat pump air-conditioning apparatus lets the refrigerant passing through the outdoor heat exchanger absorb atmospheric heat and evaporate. When an ambient temperature is low, the apparatus is required to provide a large heating capacity. The apparatus, however, cannot increase its capacity to meet this requirement because the refrigerant cannot absorb much heat from atmosphere when the ambient temperature is low.
To solve this problem, a refrigerant heating air-conditioning apparatus has been proposed. This apparatus employs a refrigerant heater in addition to a heat pump refrigerating cycle, to improve the heating capacity thereof. During a heating operation, this apparatus does not use an outdoor heat exchanger but directly heats and evaporates refrigerant with combustion heat. The apparatus discharges the latent heat of the evaporated refrigerant in an indoor heat exchanger to heat a room. During a cooling operation, the apparatus carries out a usual heat pump cooling operation.
Unlike the heat pump air-conditioning apparatus, the refrigerant heating air-conditioning apparatus does not let the refrigerant absorb atmospheric heat during the heating operation, and therefore, is not required to reduce the pressure of the refrigerant through an expansion valve.
FIG. 1 shows a Mollier diagram in which a continuous line indicates the condition of refrigerant during a heating cycle of the refrigerant heating air-conditioning apparatus, and a dotted line indicates the condition of refrigerant during a heating cycle of the standard heat pump air-conditioning apparatus. The refrigerant heating air-conditioning apparatus has no compression process seen in the heat pump air-conditioning apparatus, so that the compressor thereof serves as a refrigerant gas pump.
FIG. 2 shows a refrigerating cycle of the conventional refrigerant heating air-conditioning apparatus.
This apparatus mainly comprises a compressor 1, a four-way valve 3, an indoor heat exchanger 5, an expansion valve 7, a check valve 9, an outdoor heat exchanger 11, a refrigerant heater 13, and a two-way valve 15. These elements are connected to one another through piping.
During a heating operation, refrigerant is circulated sequentially through the compressor 1, four-way valve 3, indoor heat exchanger 5, expansion valve 7, two-way valve 15, refrigerant heater 13, and compressor 1. The expansion valve 7 is widely opened to substantially cause no pressure loss, and the outdoor heat exchanger 11 receive no refrigerant.
During a cooling operation, the refrigerant is circulated sequentially through the compressor 1, four-way valve 3, outdoor heat exchanger 11, check valve 9, expansion valve 7, indoor heat exchanger 5, four-way valve 3, and compressor 1. The two-way valve 15 is closed to supply no refrigerant to the refrigerant heater 13.
The heating capacity of this refrigerant heating air-conditioning apparatus is equal to the combustion capacity of a burner of the refrigerant heater 13 multiplied by the thermal efficiency of the refrigerant heater 13. Namely, the heating capacity of the apparatus cannot be adjusted beyond the capacity of the refrigerant heater 13. The capacity of the burner of the refrigerant heater 13 is usually adjustable at a ration of 1:3, i.e., at a minimum value of 1 to a maximum value of 3. Namely, the variable width of the heating capacity of this apparatus is 1:3.
When a required heating load is small, the variable width of the heating capacity must be supplemented by an ON/OFF operation, which deteriorates a comfortable heating condition. Compared with a continuous operation, the ON/OFF operation is disadvantageous in terms of a running cost and the durability of the burner. In particular, the ON/OFF operation causes combustion gases to condense in a heat exchanger of the refrigerant heater 13 and corrode the heat exchanger due to high acidity of the combustion gases.
To avoid the ON/OFF operation and achieve continuous heating, the air-conditioning apparatus must have a variable width of capacity of about 1:10.
When the heating operation is continued for a long time, the refrigerant gradually leaks into the outdoor heat exchanger 11 which is not in use during the heating operation, and stays therein under a liquefied state. This may cause a shortage of the refrigerant in the heating cycle. To avoid the shortage, the heating operation must be stopped to collect the leaked refrigerant. In addition, the refrigerant must be collected at the start of the heating operation. This may elongate a start-up time of the heating operation.
Since the refrigerant heater 13 is solely used without the outdoor heat exchanger 11 during the heating operation, the refrigerant heater 13 must have a larger capacity than in the simultaneous use of the refrigerant heater 13 and outdoor heat exchanger 11. This ineffective use of the outdoor heat exchanger 11 increases the size of the equipment.
When the refrigerant heater 13 uses kerosene as a fuel, the kerosene is stored in a tank, and when the kerosene in the tank is completely consumed, the heating operation is naturally stopped.
When the outdoor heat exchanger 11 is used as a heat pump for carrying out the heating operation, the outdoor heat exchanger 11 may be frosted depending on ambient conditions. In this case, the outdoor heat exchanger 11 must be defrosted by directly supplying high-temperature gasified refrigerant from the compressor 1 to the outdoor heat exchanger 11 through the-four-way valve 3. Then, the high-temperature gasified refrigerant is not supplied to the indoor heat exchanger 5. Namely, the heating operation must be temporarily stopped during the defrosting operation, and therefore, a user may not feel comfortable warmth during this period.
When operated in a cold district, the heat pump operation and refrigerant heating operation may be simultaneously carried out. In this case, the quantity of heat supplied to the indoor heat exchanger by the refrigerant heating operation is approximately four times larger than that by the heat pump operation. Accordingly, in a conventional two compressor system, the quantity of refrigerant discharged from a compressor for the heat pump operation is smaller than that from a compressor for the refrigerant heating operation. Since lubricant is evenly contained in the refrigerant fed to the compressors, the compressor for the heat pump operation with a smaller discharge of refrigerant may hold the refrigerant and lubricant, while the compressor for the refrigerant heating operation with a larger discharge of refrigerant may cause a shortage of the refrigerant and lubricant.